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Bike maintenance - John C. Kirk

Jul. 9th, 2009

01:47 am - Bike maintenance

I went along for a health assessment last Friday, and the doctor mentioned that my feet are a bit arched. I suspect that this may be because of my cycling technique: I have a tendency to press down on the pedals with the middle of my feet, rather than the balls (front).

This in turn is partly to do with the saddle position. I'm fairly tall, so I bought a telescopic seat pillar. At first I didn't use it, so I just pulled up the main seat pillar as high as it would go, then relied on the the extra pillar (even when collapsed) to give me an extra couple of centimetres. However, I've recently been pulling the telescopic pillar up a bit as well, and that does make the ride more comfortable, i.e. I can actually straighten my legs enough to get my feet into the proper position. Unfortunately, I've found that the main seat pillar has a tendency to sink down while I'm on it; it's fairly gradual (unless I hit a pothole), but I have to stop every 10-15 minutes, then get off and pull the seat up again. I'll ask the shop about that the next time I take the bike in.

Speaking of the saddle, I've also had a problem with it tilting upwards at the front, presumably because my weight has been pushing down on the back. I couldn't push it level, but last night I dug out a hex key (left over from flatpacked furniture) and adjusted the saddle. Before and after:

Riding on it today, it was a lot more comfortable, and I hope that I'm maintaining a straighter back.

While I was on a roll, I also decided to have a look at my tyres. I've had various bikes over the years, and my standard approach has always been to try squeezing the tyres with my thumb; if it feels hard, that's fine, but if it's a bit squishy then it needs more air. However, looking at the owner's manual (and the Brompton website), they're a bit more precise about tyre pressure. I have Schwalbe Marathon tyres, so that means:Front: 60 to 80 PSI, 100 PSI max.Rear: 70 to 90 PSI, 100 PSI max.

I've used electric air pumps at petrol stations, which include pressure gauges, but I've heard that it's a really bad idea to use them on bicycle tyres. (Apparently they pump air at too high a pressure, so bike tyres would explode.) On the other hand, none of the pumps I've used have ever included a pressure gauge, so how do you know when you've got the right pressure?

Doing some digging on the web, the idea seems to be that hand pumps are just for emergencies, i.e. getting a puncture while you're out and about. You then keep a "track pump" at home, which includes a pressure gauge, and use that for regular maintenance. I've never been very good at fixing punctures, even with the aid of a bucket of water, so I wouldn't fancy trying it by the side of a road. Looking at the Brompton in particular, it would be much easier just to fold it up and bring it home on the bus/train. This pump business is probably old news to most people, so does anyone else have any recommendations?

In the meantime, my back tyre seemed a bit squishy, so I figured that it would be worth pumping it up. Aside from anything else, it would be useful to figure out how my Brompton pump actually works. Unfortunately, this is where it all went a bit wrong.

When the pump is clipped onto the bike frame, it looks like this (bottom right corner):

Taking it off the bike (by pulling in one end):

One end pulls out (as you'd expect), and the plastic cap reveals a metal thing underneath:

If I unscrew the metal thing, I can then move the lever in and out:Actually, I can pull the lever out with the metal thing in place, but it's easier without it. If I screw the metal thing back on with the lever out (perpendicular to the pump), the lever automatically moves back in. So, I assume that the purpose of the metal thing is just to keep the lever in place until you want to use it.

My tyres use a Schrader valve. Quoting from the manual: "A car-type valve is used, allowing various methods of inflation. The Brompton HP pump is well suited, and can be kept on the rear frame (unless it's titanium)."

"Normal" pumps have a flexible tube on the end, so you screw that onto the valve. There's always a bit of air that escapes, but it's not too bad. This pump didn't come with any instructions, so I've been figuring it out by trial and error, and a bit of digging around the web. As I understand it, the idea is that you push the pump onto the valve, then pull out the lever to lock it in place until you've finished inflating the tyre. I've tried this, and I promptly drained all the air from the back tyre (which is now completely flat), but I can't get the pump to actually lock in place. In fact, now that the tyre is empty, if I push against the valve then it starts to go through the hole in the wheel.

I don't know whether my pump is dodgy or whether I'm just doing it wrong. Either way, it looks like I'll be taking the bus tomorrow, which is rather annoying. I'm inclined to give up on this pump as a bad job, and buy another one to replace it. Ah well, hopefully someone else can learn from my cautionary tale.

Comments:

You can get double-action hand pumps with pressure gauges - they cost around 17 quid, IIRC. You can also get the plunger-type ones for home use - stand on a footplate and press down as if you're demolishing a building. I think they probably all include pressure gauges too.

The modern bike pumps are a bit counterintuitive. You should leave the metal knob on the end of the pump nozzle, then push the whole thing onto the valve. Then pull the lever to lock the pump on. It can take a couple of goes to get it right, and with a flat tyre you'll need to grip the stem of the valve between your fingers in order to get it to go in. It will work once you get the knack - it took me a few goes when I first bought a new-style pump.

You do not need a track pump (= plunger pump that pozorvlak describes), they are expensive. Get a pressure gauge from a car accessory shop, should cost you no more than a fiver if you want to check the pressures.

You, sir, are a genius - thank you! This worked, and it also explains why some of the black rubber bits were falling out of the pump last night. I couldn't get a perfect seal (air was still hissing out while I pumped), so the tyre is still slightly squidgy if I push on it, but the bike is certainly roadworthy.

The point of the metal knob is that by partially unscrewing it you can sometimes make it fit better onto the valve. But it sounds to me like you're not pushing the pump far enough onto the valve. It is easier once the tyre is partly inflated.

Riding your bike with partially inflated tyres makes it much harder to ride, wears the tread off and eventually cracks the sidewalls. I've been there and done it!

It's usually worth getting a spare inner tube and either carrying it with you or leaving it at work. It's much easier to swap out a whole inner tube rather than repair a puncture at the side of the road. And then you can repair the old one at your leisure.

Also, not sure how well this will work on a Brompton, but toe clips will massively improve your efficiency and improve your foot placement on the pedals. What you probably want are "half clips" which just go over your toe rather than having a strap that comes over the arch of the foot. They are easy to ride with and make a big difference: http://www.cyclestore.co.uk/productDetails.asp?productID=20972

Check that your pedals can take the clips first. Or ask your bike shop.

I think you're right about not pushing the pump far enough. I pumped the tyres about half-full, then my second attempt (before I left the flat) was a bit easier. However, the bike felt really weird when I started cycling, and I could hear a regular thumping sound, so I got off and pushed it to the nearest station. I pumped up the tyres again on the train, then again en route to work, so it was just about rideable but I could see the rear tyre "splodging" out to both sides of the wheel.

I borrowed a pump from someone else at work: this is the same basic design as mine, but a different brand, and I had more luck with that. I got the air in without it hissing, but I still lost a bit when I took it off (as with my own pump). It felt ok riding back this evening, so I'd say that I'm in roughly the same position that I was in yesterday evening before I had my bright idea of pumping the tyres.

As for a track pump, I think I would benefit from having one (or at least having access to one), but I can do without one for now, so I'll put that on my "wish list".

I agree with you about inner tubes; I used to have a few for my old bike, but I gave them away because they're too big for the Brompton, so I ought to get some smaller ones.

Regarding toe clips, I think the left pedal will be the tricky one, since that folds up against the side of the bike. However, I'll ask about that at the bike shop the next time I go in (hopefully Saturday).